1. Field of the Invention
The present invention relates to an organic solvent-soluble photosensitive polyimide resin. More particularly, the present invention relates to an aromatic polyimide resin having photosensitive radicals and exhibiting satisfactory solubility in certain types of organic solvents and useful for producing a photo-set product having excellent heat resistance and electrical and mechanical properties.
The organic solvent-soluble photosensitive polyimide resin of the present invention is useful in the semiconductor field as a material for forming insulating films and passivation films for solid-state elements and as an interlaminar insulating material for semiconductor integrated circuits and multilayer printed circuit boards.
2. Description of the Prior Art
In the semiconductor industry, materials for forming insulating films and passivation films for solid-state elements and interlaminar insulating materials for semiconductor integrated circuits and multilayer printed circuit boards must exhibit excellent heat resistance and elelctrical insulating properties.
Japanese Unexamined Patent Publication (Kokai) Nos. 49-115541, 54-116216, 54-116,217, 55-45,747, 55-45,748 and 56-45,915, for example, disclose passivation films produced by a polyimide resin having a high electrical insulating property as well as high heat resistance.
Most of the polymer resins disclosed in the above-mentioned publications are insoluble in organic solvents and have no photosensitive radicals. The other polymer resins which have photosensitive radicals are produced in such a manner that carboxylic acid radicals in the polyamic acid, which is a precursor of the polyimide resin, are modified by means of amidization or esterification. The modified polyamic acid resin is converted to the corresponding polyimide resin simultaneously with a photo-setting, process or by means of post-baking procedure after a photo-setting process.
Japanese Unexamined Patent Publication (Kokai) No. 54-109,828 discloses a heat-resistant photoresist composition which comprises a mixture of an organic solvent-soluble polyimide having no photosensitve radical with a monomeric compound having photo-setting radicals and capable of photo-setting. However, this type of composition exhibits an unsatisfactory photo-setting property. Also, the resultant photo-set resin exhibits unsatisfactory heat resistance.
Generally, it was believed that conventional aromatic polyimide resins having excellent heat resistance exhibited poor solubility in organic solvents and, therefore, were useless for the formation of relief patterns on a photosensitive resin material by the process of exposing a surface of a photosensitive material to actinic rays in accordance with a desired pattern, and then dissolving the non-exposed, non-photo-set portions of the photosensitive material by means of an organic solvent.
Japanese Unexamined Patent Publication (Kokai) No. 57-131,227 discloses a process for producing a polyimide having excellent photosensitivity and heat resistance by reacting a tetracarboxylic dianhydride with a diamine compound having photo-crosslinking unsaturated double bonds, for example, diaminochalcone. This type of polyimide exhibits excellent photosensitivity. The polyimide, however, exhibits poor solubility in organic solvents and therefore takes a long time to completely dissolve in the organic solvent. It is therefore, not useful for practical formation of relief patterns on photosensitive materials.